encoding/japanese/maketables.go

// Copyright 2013 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.

//go:build ignore

package main

// This program generates tables.go:
//	go run maketables.go | gofmt > tables.go

// TODO: Emoji extensions?
// https://www.unicode.org/faq/emoji_dingbats.html
// https://www.unicode.org/Public/UNIDATA/EmojiSources.txt

import (
	"bufio"
	"fmt"
	"log"
	"net/http"
	"sort"
	"strings"
)

type entry struct {
	jisCode, table int
}

func main() {
	fmt.Printf("// generated by go run maketables.go; DO NOT EDIT\n\n")
	fmt.Printf("// Package japanese provides Japanese encodings such as EUC-JP and Shift JIS.\n")
	fmt.Printf(`package japanese // import "golang.org/x/text/encoding/japanese"` + "\n\n")

	reverse := [65536]entry{}
	for i := range reverse {
		reverse[i].table = -1
	}

	tables := []struct {
		url  string
		name string
	}{
		{"http://encoding.spec.whatwg.org/index-jis0208.txt", "0208"},
		{"http://encoding.spec.whatwg.org/index-jis0212.txt", "0212"},
	}
	for i, table := range tables {
		res, err := http.Get(table.url)
		if err != nil {
			log.Fatalf("%q: Get: %v", table.url, err)
		}
		defer res.Body.Close()

		mapping := [65536]uint16{}

		scanner := bufio.NewScanner(res.Body)
		for scanner.Scan() {
			s := strings.TrimSpace(scanner.Text())
			if s == "" || s[0] == '#' {
				continue
			}
			x, y := 0, uint16(0)
			if _, err := fmt.Sscanf(s, "%d 0x%x", &x, &y); err != nil {
				log.Fatalf("%q: could not parse %q", table.url, s)
			}
			if x < 0 || 120*94 <= x {
				log.Fatalf("%q: JIS code %d is out of range", table.url, x)
			}
			mapping[x] = y
			if reverse[y].table == -1 {
				reverse[y] = entry{jisCode: x, table: i}
			}
		}
		if err := scanner.Err(); err != nil {
			log.Fatalf("%q: scanner error: %v", table.url, err)
		}

		fmt.Printf("// jis%sDecode is the decoding table from JIS %s code to Unicode.\n// It is defined at %s\n",
			table.name, table.name, table.url)
		fmt.Printf("var jis%sDecode = [...]uint16{\n", table.name)
		for i, m := range mapping {
			if m != 0 {
				fmt.Printf("\t%d: 0x%04X,\n", i, m)
			}
		}
		fmt.Printf("}\n\n")
	}

	// Any run of at least separation continuous zero entries in the reverse map will
	// be a separate encode table.
	const separation = 1024

	intervals := []interval(nil)
	low, high := -1, -1
	for i, v := range reverse {
		if v.table == -1 {
			continue
		}
		if low < 0 {
			low = i
		} else if i-high >= separation {
			if high >= 0 {
				intervals = append(intervals, interval{low, high})
			}
			low = i
		}
		high = i + 1
	}
	if high >= 0 {
		intervals = append(intervals, interval{low, high})
	}
	sort.Sort(byDecreasingLength(intervals))

	fmt.Printf("const (\n")
	fmt.Printf("\tjis0208    = 1\n")
	fmt.Printf("\tjis0212    = 2\n")
	fmt.Printf("\tcodeMask   = 0x7f\n")
	fmt.Printf("\tcodeShift  = 7\n")
	fmt.Printf("\ttableShift = 14\n")
	fmt.Printf(")\n\n")

	fmt.Printf("const numEncodeTables = %d\n\n", len(intervals))
	fmt.Printf("// encodeX are the encoding tables from Unicode to JIS code,\n")
	fmt.Printf("// sorted by decreasing length.\n")
	for i, v := range intervals {
		fmt.Printf("// encode%d: %5d entries for runes in [%5d, %5d).\n", i, v.len(), v.low, v.high)
	}
	fmt.Printf("//\n")
	fmt.Printf("// The high two bits of the value record whether the JIS code comes from the\n")
	fmt.Printf("// JIS0208 table (high bits == 1) or the JIS0212 table (high bits == 2).\n")
	fmt.Printf("// The low 14 bits are two 7-bit unsigned integers j1 and j2 that form the\n")
	fmt.Printf("// JIS code (94*j1 + j2) within that table.\n")
	fmt.Printf("\n")

	for i, v := range intervals {
		fmt.Printf("const encode%dLow, encode%dHigh = %d, %d\n\n", i, i, v.low, v.high)
		fmt.Printf("var encode%d = [...]uint16{\n", i)
		for j := v.low; j < v.high; j++ {
			x := reverse[j]
			if x.table == -1 {
				continue
			}
			fmt.Printf("\t%d - %d: jis%s<<14 | 0x%02X<<7 | 0x%02X,\n",
				j, v.low, tables[x.table].name, x.jisCode/94, x.jisCode%94)
		}
		fmt.Printf("}\n\n")
	}
}

// interval is a half-open interval [low, high).
type interval struct {
	low, high int
}

func (i interval) len() int { return i.high - i.low }

// byDecreasingLength sorts intervals by decreasing length.
type byDecreasingLength []interval

func (b byDecreasingLength) Len() int           { return len(b) }
func (b byDecreasingLength) Less(i, j int) bool { return b[i].len() > b[j].len() }
func (b byDecreasingLength) Swap(i, j int)      { b[i], b[j] = b[j], b[i] }